Process of making pitch



Unite PROCESS OF MAKING PITCH Filed Feb. 14, 1958, Ser. No. 715,366

3 Claims. (Cl. 208-39) This invention relates to a method for theproduction of petroleum pitches and is particularly concerned with thepreparation of petroleum pitches from crude oils of low asphaltenecontent.

In the refining of petroleum oils it is desirable to obtain the highestpossible yields of distillate oils such as gasoline, kerosene andheating oils because of the higher prices received for those products.The yield of the distillate oils is increased by making deep cuts intothe crude by vacuum distillation to separate as much of the distillablepo'rtion of the crude as possible from the residual fractions. Theheaviest distillate fractions separated in the vacuum distillation arethe heavy gas oils ordinarily used as charge stock to catalytic crackingunits for conversion to lighter fractions, principally gasoline.Residues from vacuum distillation are used in the preparation of heavyfuel oils. As higher flash temperatures are used in the distillation,the residual pro'ducts become heavier and more viscous. In order toproduce a heavy fuel oil meeting the A.S.T.M. viscosity specificationsfor a No. 6 fuel oil, the residual products from deep vacuumdistillation must be blended with lighter oils, designated as cutteroils. Because of the low market value of the heavy fuel oil, theblending of cutter oils with residual products to produce a heavy fueloil results in a reduction of the ultimate market value of the cutteroils.

One method of increasing the market value of the products obtained fromthe crude oil is to prepare a solid petroleum pitch as a residualproduct. In such processes no cutter oil is required; hence, theultimate yield of distillate products is increased. The petroleumpitches are of principal value as a solid fuel and when used as such areoften subjected to substantial pressures and temperatures above about130 F. in storage. To prevent fusion of the pitch into a solid masswhile in storage, a pitch having a ring and ball (A.S.T.M. E28-51T)softening point of about 300 F. and preferably 325 F. or higher has beenrequired when prepared by the processes heretofore available. Thoseprocesses were either restricted to the treatment of crude oils of highasphaltene content, or demanded extremely severe operating conditions toproduce a pitch having the necessary fusion characteristics from crudeoils of low asphaltene content. The extremely severe conditions neededto produce the high softening point pitches from the crude oils of lowasphaltene content favor increased coking and fouling of equipment andthus impair the operability of the process.

This invention resides in a process of excellent operability for theproduction of a petroleum pitch having a high incipient fusio'ntemperature by visbreaking a bottoms fraction of a crude oil of lowasphaltene content, fractionating the visbreaker product to produce avisbreaker tar and then subjecting the visbreaker tar to a secondvisbreaking step performed in the absence of virgin petroleum fractions.The final petroleum pitch product is then obtained as a bottoms productfrom the atmospheric distillation of the eflluent from the second StatesPatent "ice visbreaking operation. An important advantage of the processof this invention is the higher incipient fusion temperature of a pitchof a given ring and ball softening point prepared by this methodcompared with pitches of corresponding ring and ball softening pointprepared by the processes heretofore available. Because of this uniquerelationship between the incipient fusion temperature and the ring andball softening point, pitches satisfactory for use as solid fuels canhave ring and ball softening points as low as 250 F. when prepared bythis invention.

In the drawings:

Figure 1 is a diagrammatic flow sheet of the process for the preparationof a petroleum pitch by the method of this invention.

Figure 2 is a graph showing the incipient fusion temperature ofpetroleum pitches of given ring and ball softening points as comparedwith pitches produced by processes heretofore available.

The charge stock for the process of this invention can be any petroleumcrude oil which ordinarily would be used for the preparation of pitches.This process is particularly valuable for the preparation of pitchessuitable for use as solid fuels from low asphaltene content crude oils,such as those obtained from Kuwait, West Texas and Mid-Continent fields.Other methods, for example, the method described in application SerialNo. 416,634 of Harold Beuther and Richard G. Goldthwait, filed March 16,1954, now US. Patent No. 2,850,436, are preferred for the preparation ofpetroleum pitches from crude oils of high asphaltene content.

Referring to Figure l of the drawings, a topped crude oil from anatmospheric tower, not shown, in which, for example, a furnace oil andlighter fractions have been removed, is delivered through line 10 to avacuum tower l2. Vacuum tower 12 is operated at a flash temperature,corrected to atmospheric pressure, above about 940 F. and may range upto a corrected temperature of about 1050 F. Higher corrected flashtemperatures can be used, but ordinarily are not used because of theincreased costs incurred in obtaining them without excessive cracking inthe distillation operation. A heavy gas oil suitable for use as acatalytic cracking charge stock top of the vacuum tower 12 and a bottomsfraction containing virgin heavy residual oils is delivered through line16 from the bottom of the vacuum tower 12. Ordinarily steam is injectedthrough a line such as line 18 into the bottom of the vacuum tower toaid in the stripping of volatile components from the bottoms fraction.

The vacuum reduction of the topped crude oil that occurs in vacuum tower12 is a normal operation for the preparation of a visbreaking chargestock in modern refinery practice. The depth of reduction of some crudeoils may be limited by the maximum metals and carbon residue permissiblein the gas oil delivered overhead from the vacuum tower. In the vacuumdistillation of some crude oils, the metals co'ntent or the carbonresidue of the overhead from the vacuum tower will increase rapidly asthe depth of the cut into the crude oil is increased. Extremely deepvacuum reduction of such crude oils is not feasible. Propanedeasphalting of the topped crude oil also can be used to produce ahighly asphaltenic residue for charging to the first visbreaker.

The bottoms fraction from the vacuum tower is delivered through line 16to the coils 20 of a first visbreaker furnace 22 in which the bottomsfraction is heated to a furnace outlet temperature of about 825 to 1000F. The pressure in the coils 20 of visbreaker furnace 22 is in the rangeof about 50 to 1000 p.s.i.-g. and the volume of the coil above 750 F. inthe range of about 0.016 to 0.050 cubic foot per barrel of through- 3put per day. The first visbreaking operation is a oncethrough crackingoperation of the residual oils at a severity such that about 8 to 17%debutanized 400 and point gasoline is produced. Recycle of intermediatefractions of the first visbreaker product, for example, light gas oils,may be employed.

The product from the first vibreaker furnace 22 is delivered throughline 24 into an intermediate distillation tower 26 in which a heavybottoms fraction, herein designited as a visbreaker tar is separatedfrom lighter oils for further treatment. The intermediate distillationmay vary widely from a mild atmospheric distillation to a vacuumdistillation. In the mild atmospheric distillation the visbreaker tar isessentially a furnace oil-free residue, produced as a bottoms productand discharged from the tower 26 through line 28. The mild atmosphericdistillation may be defined as one adapted to remove a furnace oil 90%of which boils below about 600 F. Ordinarily the flash temperature inthe mild atmospheric distillation will be in the range of 650 to 700 F.Steam can be injected into the distillation tower 26 to aid in thestripping of light fractions from the bottoms removed from the tower.Similarly, in a mild atmospheric distillation a reboiler may be used toincrease stripping in the lower part of the tower 26. I

A deep atmospheric distillation also may be performed as an intermediatedistillation between the first and second visbreaking step. In a deepatmospheric distillation a distillate gas oil fraction having a 90%boiling point in the range of 650 to 800 F. can be obtained. In a deepatmospheric distillation, steam is usually added at a moderate rate upto about 50 pounds per barrel of first visbreaker product, andpreferably about pounds per barrel, to improve the stripping.

The intermediate distillation also can be a vacuum distillation step.The vacuum distillation of the effluent from the first visbreaker 22 hascertain advantages in the reduction of tendencies to form coke in thesecond visbreaking step but suffers the disadvantage of increased costbecause of the size of the unit and steam requirements for a vacuumdistillation. Generally, the incipient fusion temperature of a petroleumpitch of a given ring and ball softening point prepared with anintermediate vacuum distillation is higher than of pitches of the samering and ball softening point prepared with other intermediatedistillation steps. In the vacuum distillation a flash temperature of940 F., corrected to 760 mm. of mercury absolute pressure, up to about1030 F. is used.

Regardless of the manner of performing the intermediate distillation,the visbreaker tar charged to the second visbreaking step is a veryheavy residue which has had a single pass through a visbreaker. Furnaceoil, or gas oil, and lighter fractions have been separated from thevisbreaker tar. The gravity of the visbreaker tar, even when the firstvisbreaker product is subjected to only a mild atmospheric distillation,is less than about 5' A.P.I.

The visbreaker tar from the distillation tower 26 is delivered throughline 28 to the coil 30 of a second visbreaker 32 in which the tar isheated to a coil outlet temperature in the range of 820 to 1000 F. Theseverity of the visbreaking in coil 30 is normal for conventionalvisbreaking of vacuum reduced crudes. About 5 to of the charge to thesecond visbreaker coil is converted to 400 F. end point gasoline. Thetemperature, pressure, and coil volume for the second visbreaking stepare substantially the same as corresponding conditions in the firstvisbreaking step.

The product from the visbreaker coil 30, herein referred to as thesecond visbreaker product, is delivered through line 34 into anatmospheric flash distillation tower 36. Gas oil and lighter fractionsare removed as distillate products from tower 36 and the petroleum pitchis discharged as a bottoms product through line 38. The flashtemperature in tower 36 ranges from about 700 F.

up w a maximum of about 825 F. and o to so, preferably 25 to 50, poundsof steam per barrel of oil are charged to the tower. The maximum flashtemperature used in tower 36 is limited by the formation of coke in thetower. A portion of the steam may be injected through quench line 40 toquench the second visbreaker product discharged from coil 30 and theremainder of the steam is added directly through line 42 into the bottomof the tower 36. A portion of the distillate fractions separated intower 36 may be recycled through visbreaker 30, or used as qu ench, butthe visbreaker operation is once-through for the residual fraction. Aheavy gas oil, suitable for blending with No. 6 fuel oils, and lighterfractions are obtained as products in addition to the pitch.

An important advantage of this invention is the higher incipient fusiontemperature of pitches of a given ring and ball softening point ascompared with incipient fusion temperature of pitches of the same ringand ball softening point prepared by processes in which there is asingle visbreaking step. The incipient fusion temperature is defined asthe minimum temperature at which adhesion of pitch particles occurs whenthe pitch particles are subjected to a pressure corresponding to thepressure exerted by a pile of pitch 40 feet high. Determinations of theincipient fusion temperature were made by placing pitch particles in acylinder and applying a pressure of 13.3 p.s.i. to a piston movable inthe cylinder. The cylinder was placed in a bath and the temperatureraised gradually until incipient fusion occurred. At the incipientfusion temperature there was adhesion of the pitch particles at theinterface between the pitch and the piston only, but not throughout thecylinder. The adhesion was predominantly to the piston, and, at most,extended about Va inch into the pitch. Inst below the temperature ofincipient fusion, there was no adhesion of pitch particles. Just abovethe incipient fusion temperature, at a temperature of about 5 to 10 F.higher than the incipient fusion point, adhesion occurred throughout thecylinder but when the pitch particles were cooled and broken up,separation occurred predominantly at the original interfacial surfaces.

Referring to Figure 2 of the drawings, curve 46 shows the relationshipbetween the incipient fusion temperature and the ring and ball softeningpoint of pitches prepared from Kuwait crude oil by the two visbreakingstep method of this invention. Slight variations from curve 46 willoccur and will depend upon the type of intermediate distillation used.The curve identified by reference numeral 48 shows the relationshipbetween the incipient fusion temperature and the ring and ball softeningpoint of pitches prepared by a single visbreaking of the residue fromthe vacuum reduction of Kuwait crude oil followed by the deep vacuumreduction of the visbroken residue to produce the pitch as a bottomsproduct.

It will be seen from Figure 2 that the incipient fusion temperature of apitch prepared by the two visbreaking step process of this invention isabout 50 higher than the incipient fusion temperature of a pitchprepared by a process employing a single visbreaker and having the samering and ball softening point. Conversely, a pitch prepared according tothis invention having an incipient fusion temperature of 130 F. has aring and ball softening point above F. lower than the ring and ballsoftening point of a pitch of the same incipient fusion temperatureprepared in a process using a single visbreaking step.

EXAMPLE 1 A Kuwait crude oil was topped in an atmospheric distillationtower and the bottoms fraction from the atmoshperic distillation flashedin an equilibrium distillation at a temperature corrected to 760 mm. ofmercury absolute pressure, of approximately 1030" F. The bottomsfraction from the vacuum flash distillation was charged to a visbreakercoil maintained at a pressure of about 275 p.s.i. The outlet temperatureof the vis- 5 breaker coil was about 915 F. and the coil volume above750 'F. was about 0.027 cubic foot per barrel of throughput per day. Thevisbreaking step produced 11.4%, by volume of the charge stock thevisbreaker, of 400 F.

distillation. The visbreaker tar was cracked in a second visbreaker stepat a pressure of 275 p.s.i.g., a furnace coil volume above 75 0 F. of0.027 cubic foot per barrel of throughput per day, and a furnace outlettemperaend point gasoline. ture of 875 F. The product from the secondvisbreaker The visbreaker product was distilled in an atmospheric wasflashed at a temperature of 800 F. in an atmosdistillation to separate afurnace oil and lighter fracpheric distillation employing 47.9 pounds ofsteam per tions from a visbreaker tar having a gravity of 2.9 A.P.I.barrel of reduced crude charge to the second visbreaker. The furnace oilhad a distillation curve such that 90% The bottoms from the atmosphericdistillation was a of the furnace oil distilled over at 591 F. A portionpitch having a ring and ball softening point of 285 F. of the furnaceoil-free visbreaker tar was then passed and an incipient fusiontemperature of 170 F. through a second visbreaker gt a furnace outlettem- EXAMPLE 5 perature of approximately 875 F. A furnace pressure of275 p.s.i.g. and a furnace coil volume above 750 F. A p n f he v sbreker tar from the vacuum disof 0,027 cubic foot per barrel of throughputper day tillation Of the fiI St visbreaker product described in E X-were employed in the second visbreaker. The eifiuent ample 4 wassubiected to a second vlsbreakmg t p at from the visbreaker was flashedat a temperature of 803 the salhe furnace Pressure and C volume above750 F. in an atmospheric distillation tower using a total of as 111 p 4but at a l p 0f 47.8 pounds of steam per barrel of reduced crude chargeThe Product h f eeeehd Vlshfeakel was flashed to the second visbreaker,A pitch having a ring d an atmospheric distillation at a temperature of801 F., ball softening point of 292 F. and an incipient fusion 1151118Pounds of Steam p barrel of reduced Cr temperature f 170 F, was d chargeto the second visbreaker to produce as a bottoms EXAMPLE 2 product apitch having a ring and ball softening point of 349 F. and an incipientfusion temperature of 230 F. A sample of the furnace oil-free visbreakertar of Example 1 Was subjected to a second visbreaking step EXAMPLE 6with th sam dition 35 E l 1 except h the A portion of the visbreaker tarfrom the vacuum disoutlet temperature was approximately 915 F, Thdtillation of the product of the first visbreaker described uct from thevisbreaker was flashed at a temperature 111 Example 4 was Suhlected to aSecond vishl'eakihg p of 801 F. using a steam rate of 49.1 pounds perbarrel at a telTlPel'etllfe 0f and at the Same Co ditions of reducedcrude charge to the second visbreaker. The 9 furnace Pressure and ellV0111Ine above as pitch produced had a ring and ball softening point of111 Example The secohd Y h h Product was then 346 F, d an i i i f itemperature f 230 F. flashed in an atmospheric distillation at atemperature of 803 F. using 31.6 pounds of steam per barrel of EXAMPLE 3reduced crude charge to the second visbreaker. The A sample of the firstvisbreaker product described bottoms product from the atmosphericdistillation was in Example 1 was subjected to a deep atmospheric disaPItch h a and ban Softehlhg P of tillation to produce a -1.0 A.P.I.visbreaker tar as a and an mclplent fuslon temperature 5 bottoms productand separate thcrefrom a gas oil hav- The results 0f the pfoeessesdescribed In Examples 1 ing a 90% distillation point at 655 F., andlighter 40 through 6 are Presented In Table T able 1 Volume ASTM PercentE28-51T Incipient 400 F. Flash Steam, Ring and Fusion Example No. Chargeto2nd visbreaker End Temp., lb./bbi. Ball Point,

Point F. Softening F. Gasoline Temp,

Furnace Oil-Free Tar 6.2 803 47.8 292 170 do 9. 6 801 49.1 346 230 DeepAtmospheric Distilled Tar 5. 5 795 51.6 305 175 Vacuum Distilled Tar 6.2 800 47. 9 285 170 do 9.8 801 50.6 349 230 .do 9.9 803 31.6 351 255EXAMPLE 4 A sample of the product from the first visbreaker stepdescribed in Example 1 was subjected to a vacuum distillation underconditions to separate a visbreaker tar having a specific gravitycorrected to 77 F./77 F. of 1.089. A gas oil, 88% of which boiled below1000 F., corrected to 760 min. of mercury, and lighter fractions wereseparated from the visbreaker tar in the vacuum This invention providesa method for the preparation of petroleum pitches from petroleum crudeoils of low asphaltene content. Pitches having high ring and ballsoftening points can be prepared without using such severe visbreakingand vacuum flash distillation conditions that excessive amounts of cokeare formed. Hence, the process of this invention has excellentoperability characteristics, i.e. it can be operated for long periodswithout shutting down to clean coke from the equipment. Moreover, thevery high incipient fusion temperatures of the pitches prepared by theprocess of this invention makes it unnecessary .for the pitches to haveextremely high ring and ball softening points to be useful as solidfuels.

We claim:

1. A process for the preparation of a petroleum pitch having a ring andball softening point above about 250 F. and an incipent fusiontemperature above about F. comprising flashing a topped crude oil undervacuum fraction at conditions to produce about 8 to 17% 400 F. end pointgasoline, distilling the visbreaker product in an atmosphericdistillation to separate furnace oil and lighter fractions and produce avisbreaker tar as a residual fraction, passing the visbreaker tar in theabsence of virgin petroleum fractions through a second visbreaker inwhich about to 15% 400 F. end point gasoline is formed, flashing thesecond visbreaker product in an atmospheric distillation at atemperature in the range of 700 to 825 F. in the presence of steam toproduce the pitch as a bottoms product.

2. A process as set forh in claim 1 in which the distillation of thefirst visbreaker product produces a visbreaker tar having a gravitylower than about 5 A.P.I.

3. A process for the preparation of petroleum pitch having a ring andball softening point above about 250 F. and an incipent fusiontemperature above about 130 F., comprising reducing a topped crude by aprocess selected from the group consisting of vacuum distillation andpropane deasphalting to produce a heavy, highly asphaltenic residue,passing the residue through a visbreaker coil in a once-through,coil-only visbreaking of the residue at a temperature in the range of825 F. to 1000 F. and a pressure in the range of about to 1000 p.s.i.g.to produce about 8 to 17% 400 F. end point gasoline, distilling thevisbreaker'product in an atmospheric distillation to produce as abottoms fraction a visbreaker tar having a gravity less than 5 A.P.I.,passing the visbreaker tar in the absence of virgin residual petroleumfractions through a second visbreaker in which about 5 to 15% 400 F. endpoint gasoline is formed, and flashing the second visbreaker product inan atmospheric distillation at a temperature in the range of 700 to 825F. to produce the pitch as a bottoms product.

References Cited in the file of this patent UNITED STATES PATENTS2,305,440 Noel Dec. 15, 1942 2,687,986 Jennings et al. Aug. 31, 19542,796,388 Beuther et al. June 18, 1957 2,847,359 Beuther et al. Aug. 12,1958 2,865,835 Owen Dec. 23, 1958

1. A PROCESS FOR THE PREPARATION OF A PETROLEUM PITCH HAVING A RING ANDBALL SOFTENING POINT ABOVE ABOUT 250* F. AND AN INCIPENT FUSIONTEMPERATURE ABOVE ABOUT 130* F. COMPRISING FLASHING A TOPPED CRUDE OILUNDER VACUUM AT A FLASH TEMPERATURE, CORRECTED TO 760 MM. OF MERCURYABSOLUTE PRESSURE, ABOVE ABOUT 940*F. TO PRODUCE A HEAVY BOTTOMSFRACTION, VISBREAKING THE HEAVY BOTTOMS FRACTION AT CONDITIONS TOPRODUCT ABOUT 8 TO 17% 400* F. END POINT GASOLINE, DISTILLING THEVISBREAKER PRODUCT IN AN ATMOSPHERIC DISTILLATION TO SEPARATE FURNACEOIL AND